TARBELA RESERVOIR, Pakistan -- "I think, after terrorism, the biggest threat we have is the environmental decay."

Tariq Yousafzai, a water and environmental engineer with detailed knowledge of his country's water infrastructure, sees evidence of climate change in the flood disaster that inundated one-fifth of his country. But a more immediate concern of his is the massive deforestation that has silted up the waterways and left Pakistan more vulnerable to storms than ever.

The scene at this reservoir created by the Tarbela Dam and in areas to its north vividly shows what he's talking about. Long after the rains ended, the water level is still almost even with the rim of the dam, seemingly ready to spill over at any moment. Equally striking is the murky color of the water itself.

The color you see while flying over this man-made lake, nearly 100 square miles in area, isn't the azure blue more typical of rivers like the Indus, fed early by snowmelt and glacial runoff in high altitudes. Rather, the water is a soupy gray mixture, something like wet concrete.

A glance at the hillsides nearby immediately tells you why -- they've been almost completely stripped of their tree cover. The clear-cutting Yousafzai describes is seen throughout northern and central Khyber Pakhtunkhwa province and extends almost to the Kashmir border. Massive quantities of silt that erode from the hills and mountains with each rain have given the Indus a gray hue well into the rugged northern country.

"Unfortunately, there is very little attention towards the accumulating environmental problems," Yousafzai said. He blames global warming for roughly a third of the flooding this summer. The rest was caused by deforestation, poor infrastructure development in the north, and engineering problems in irrigation systems in the south from mismanagement and neglect, he contends.

The government acknowledges that loss of tree cover has led to a serious problem. Compounding this problem is the lack of any plan, from either central or regional government authorities, to deal with the silting up of rivers and reservoirs. Environmental decay and a lack of maintenance of some flood barriers contributed heavily to the deluge, especially in the south.

"Our [environmental] degradational costs are increasing year by year, and eventually, time will come when it will be nearly impossible to manage them," said Hameed Ullah Jan Afridi, Pakistan's minister of environment. "So serious consideration is required."

Man-made causes include the 'timber mafia'

But government officials believe deliberate human degradation of Pakistan's environment, along with a string of failings in engineering projects downstream from Tarbela Dam, made the 2010 summer flooding only about 30 percent worse than it otherwise would have been, even as Yousafzai and others say it made the flooding 70 percent worse. While that debate rages on, officials are preparing for a Friday release of an assessment on damage to water and irrigation networks from the floods.

Preliminary estimates suggest that just under $200 million is needed to get the system back into shape. Looking ahead at rebuilding, however, most officials say even more expensive dams and diversion canals, and not less expensive ones, will be needed to protect the nation from the unprecedented downpours meteorologists fear will arrive about every decade, as some climate change models allude to.

Islamabad plans to ask the international community to pay for much of these, citing the responsibility of the rich world to help developing nations like Pakistan adapt to the feared ravages of climate change.

At the same time, ministers and civil servants are also promising a campaign of environmental stewardship, to restore forests and crack down on illegal logging that is to blame for almost three-quarters of the deforestation problem. Pakistani environmentalists, citing corruption and entrenched political interests, remain skeptical.